A two-stage heat treatment that makes medium-carbon and alloy steel fasteners strong and tough. Parts are heated to about 850 to 900 C, quenched in oil or polymer to form martensite, then tempered at a high temperature that trades some hardness for ductility. Strength grades such as SAE Grade 5 and 8 and metric 8.8 and up set minimum tempering temperatures so parts cannot ship too hard and brittle.
Quench and temper on the 10.9 lot came back 41 Rockwell C, the temper was short, back in the furnace before anything ships.
Also heard as
- Q&T
- hardened and tempered
- through-hardening
Related terms
Property class
The metric strength grade of a bolt or nut, stamped on the head as a number such as 8.8, 10.9 or 12.9.
SAE grade
The inch bolt strength system, chiefly Grades 2, 5 and 8, identified by radial lines on the head.
Hydrogen embrittlement
Delayed brittle cracking of hard steel fasteners caused by hydrogen absorbed from plating, cleaning or corrosion.
Bake
To heat plated high-strength fasteners soon after plating so absorbed hydrogen escapes before it cracks them.